Why a wide-band oxygen sensor on the RX8??
 

I'm really curious to see if anyone has an idea why our RX8 are fitted with a wide-band lambda sensor considering it apparently (=as far as I have observed with my sCANalyser) only runs in close loop at a stoichiometric AFR. Therefore, a switching HEGO would have done the job as well, if not better.

I have one or two ideas, but I'd like to hear your opinion about it too.

Thanks,

Fabrice

My thoughts:
1. Hardware or software limitations with the PCM
2. Flexibility - maybe Mazda thought there may be some need to do some behaviour based on wideband O2 readings (e.g. looking at cat temp + current AFR to determine dump rate of extra fuel for cooling purposes)

Useful given it's a car sold to a range of markets, with different emission regs in each (potentially)

I had similar thoughts, but expressed differently :

1- Initial program assumption might have included some relatively lean burn operation or close loop WOT running but it was canceled for XYZ reason during the program but they had to remain with the same hardware and software (PCM) for cost reasons.

2- Diagnostics : it might be used by the OBD system to monitor the engine management, and maybe to better infer the catalyst temperature.

The Mazda RX8 Training course (borrowed from my dealer) does not give any answer either.

I will also ask the question to some Ford engineers I know.

Fabrice

Emissions were such a issue with the previous cars I'm sure it just helps the PCM better manage the emissions profile and keep the car operating in a clean manor.

No that's the point, it doesn't do anything that a narrow bang / switching HEGO could do (better).

F

Because the A/F target is closer to 12.5:1 in closed loop at some load points.

I haven't observed that. At which speed and loads did you see that?

F

4800 RPM to 6250 at 10% to 35% absolute load after 10 to 15 seconds at vehicle speeds over 35 MPH.

Thanks MM, I will that as soon as I can.

F

Mmmh, can't see it on mine. Here are some data :

- RPM : 5500 to 6000 rpm
- Lambda : slightly rich
- Load_abs : between 20 and 25%
- Fuel System Status : OPEN LOOP!

Don't seem to be running in close loop. Will do some specific runs tomorrow.

Fabrice

I don't see the open loop flag at all on my car until I hit absolute load numbers above 35%.
Above 35%, it is dependant on vehicle speed.

country differences in pcm programming?